As far as i could find, the only possible frontend for Orleans it is ASP.NET. Is there any way to have not .net frontend?
The api specification is public, you can implement in the language that you prefer, But as it relies in .net binary serialization and primitives, I don't think is a wise decision. If you want to connect from other languages, the prefered approach it's to use a webapi as a proxy between the orleans cluster and the rest of your services. There is even a automatic API which publishes all orleans public methods as http endpoint in the contributions packages.
What are you trying to do?